Once per game, during the Remaining Moves sub-phase, models with this rule may drop rocks unless they are fleeing or have declared a charge that turn. All models in a unit must drop rocks at the same time.
To drop rocks, select one unengaged enemy unit that the Terradons moved over in that turn. That target immediately suffers D3 S 4 hits for each Terradon in the unit, distributed as for shooting attacks.